Biorheology - Volume 5, issue 4

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Biorheology is an international interdisciplinary journal that publishes research on the deformation and flow properties of biological systems or materials. It is the aim of the editors and publishers of
Biorheology to bring together contributions from those working in various fields of biorheological research from all over the world. A diverse editorial board with broad international representation provides guidance and expertise in wide-ranging applications of rheological methods to biological systems and materials.

The aim of biorheological research is to determine and characterize the dynamics of physiological processes at all levels of organization. Manuscripts should report original theoretical and/or experimental research promoting the scientific and technological advances in a broad field that ranges from the rheology of macromolecules and macromolecular arrays to cell, tissue and organ rheology. In all these areas, the interrelationships of rheological properties of the systems or materials investigated and their structural and functional aspects are stressed.

The scope of papers solicited by
Biorheology extends to systems at different levels of organization that have never been studied before, or, if studied previously, have either never been analyzed in terms of their rheological properties or have not been studied from the point of view of the rheological matching between their structural and functional properties. This biorheological approach applies in particular to molecular studies where changes of physical properties and conformation are investigated without reference to how the process actually takes place, how the forces generated are matched to the properties of the structures and environment concerned, proper time scales, or what structures or strength of structures are required.

Biorheology invites papers in which such 'molecular biorheological' aspects, whether in animal or plant systems, are examined and discussed. While we emphasize the biorheology of physiological function in organs and systems, the biorheology of disease is of equal interest. Biorheological analyses of pathological processes and their clinical implications are encouraged, including basic clinical research on hemodynamics and hemorheology.

In keeping with the rapidly developing fields of mechanobiology and regenerative medicine,
Biorheology aims to include studies of the rheological aspects of these fields by focusing on the dynamics of mechanical stress formation and the response of biological materials at the molecular and cellular level resulting from fluid-solid interactions. With increasing focus on new applications of nanotechnology to biological systems, rheological studies of the behavior of biological materials in therapeutic or diagnostic medical devices operating at the micro and nano scales are most welcome.

Abstract: The velocity profile of flowing blood has been variously suggested as (i) smooth and continuous (the classical view) and (ii) discontinuous in a step-wise fashion (the sigma view). Interferometric observations of red blood cell velocity variations, in a near-wall vicinity at small velocities, were compared to limiting values predicted from continuous velocity profile considerations coupled with a plasma no-slip boundary condition. Some 92.5 percent of the observations are in accord with the assumed continuity. Thus scant support is given the sigma model concept. An appendix provides practical notes on blood flow interferometry.

Abstract: A simple and inexpensive low-shear capillary viscometer has been developed. It comprises a coiled plastic capillary 1 mm in dia. and 4–8 m long. A pressure difference is imposed on the capillary by means of a rubber air inflation bulb and is read on an ordinary manometer. The flow rate is measured by timing the blood meniscus between two divisions in a graduated tube. Use of a very long capillary allows one to attain very small shear rates while employing large pressure differences, thus ensuring that surface tension effects are negligible. The range of relative velocity (U ¯…= 4 Q ˙ / π D 3 , tube diameters/sec) is from 0.1 to 50 sec−1 . The instrument requires a sample volume of less than 10 ml and its extreme simplicity, both in construction and operation, is emphasised. Theoretical analysis indicates that errors due to using a coiled capillary and operating under unsteady-state conditions are completely negligible.
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Abstract: Direct measurements of the compressibility of whole blood have been made over the physiologic range of pressures by means of a specially designed pressure chamber in which the sample is maintained at constant temperature within very close tolerances. Results are presented for canine arterial blood and for human venous blood of various hematocrits. It is found that the compressibility of blood is nearly that of distilled water and is independent of hematocrit.

Abstract: Model experiments were conducted in which a suspension of rigid spherical particles of neutral buoyancy in a highly viscous Newtonian fluid was passed through simulated idealized stenoses in a rigid tube under a steady pressure gradient. The ranges of Reynolds numbers (0.3–50), ratio of orifice diameter to tube diameter (1/4–3/4), and particle concentration (0–44 per cent) were selected to compare with values found in the living system. It was found that the pressure drops across the stenoses exceeded the theoretical values somewhat, even with no particles present. The pressure drop increased systematically with particle concentration until particle flow through the…stenosis ceased. The flow rate then diminished rapidly as particles accumulated on the upstream side. A Venturi-type stenosis produced considerably higher pressure drops than a corresponding orifice at the same flow rate. However, the Venturi-type stenosis permitted flows with higher particle concentration without plugging. So long as no plugging occurred, it was found that the increase in pressure drop with particle concentration agreed favorably with existing theory if one considers the suspension as a continuum of increased viscosity.
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Abstract: The behavior of linear visco-clastic materials may be approximated by differential equation of motion whose solution makes it possible to establish a relation between visco-elastic parameters obtained from stress relaxation studies and those obtained from oscillatory studies. Living tissues behave like linear visco-elastic materials under some conditions so that parameters may be determined from the two kinds of studies and compared with each other to establish the standard linear solid as a model. This study succeeds in showing the model to be suitable under a limited range of conditions for a variety of viable tissues tested in vitro .

Abstract: Superhelices arise by the tension of two or more intertwined helices with slightly different pitches. Super helices made of steel-wire which rotate in honey show either a rotation of the rigid helix (arrows R in Fig. 4b) a rotation under flexible deformation (arrows r in Fig. 4c) or a combination of these two kinds of rotation (arrows R and r in Fig. 4d). The number of the actual revolutions per second (r /sec) is much higher in the latter case than the number of revolutions of the superhelix (R /sec). The transverse waves appearing here (arrows…S in Fig. 4d) show a retardation caused by the resistance forces of the medium and are similar in a striking manner to the transveral waves running along protoplasmic fibrils and flagella. Therefore the generation of these waves may be explained by the revolutions of flexible superhelices and some variability in their inner tension. A periodic contact takes place of those particles which adhere at corresponding sites of the two intertwined helices (p 1 − q 1 . p 2 − q 2 , in Fig. 5c) when the superhelix rotates under flexible deformation.
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Abstract: Critical Reynolds numbers were experimentally determined for blood samples in steady flow in tubes. The values of these critical Reynolds numbers increased as the tube diameters decreased. It is suggested that the behavior of the cell-depleted plasma zone at the wall has an influence on the critical Reynolds numbers.